Trunking communication is a special dispatching communication method, providing commanding and dispatching communication functions via a simplex communication mode. Trunking communication is widely applied to various fields, such as medical care and rescue, transportation, municipal administration, manufacturing and mining industries, public security, and military. Professional digital trunking communication based on the Code Division Multiple Access (CDMA) technology has the advantages of high rate of frequency utilization, wide coverage, great user capacity, clear sound, energy efficiency, environmental friendliness, high conversation confidentiality, among others. FIG. 1 shows a schematic diagram of a network structure of a trunking communication system. As shown in FIG. 1, the network structure of the trunking communication system is generally composed of a Mobile Station (MS), a Base Station Sub-System (BSS), a Mobile Switching Sub-system (MSS), a Dispatching Sub-System (DSS), a Packet Data Service Sub-system (PDSS) and an Operation and Maintenance Centre (OMC).
Trunking communication involves two concepts: group and dispatching area, wherein a group is a logic collection of certain number of group members, and a group call initiated from each member can be heard by all the group members. A dispatching area is defined by dividing the network coverage of a communication system, and the minimum unit of a dispatching area may be a cell of the base station. A dispatching area of a group may also include multiple cells. Based on the setting of the dispatching area, a trunking communication system generally allows two types of group calls: non-dispatching area group calls and dispatching area group calls. Relatively speaking, non-dispatching area group calls have no restrictions and are like regular group calls. Restrictions for dispatching area group calls include:
(1) a user outside the dispatching area cannot be called;
(2) a user outside the dispatching area can initiate a call; and
(3) a call will not be dropped when a user moves outside the dispatching area during the call process.
Normally, it may be required that a group member can only be called within a certain geographical region, namely, only users in this region can be called. Setting dispatching area can realize this purpose and has the following advantages:
(1) some special services require communications to be confidential and only certain people in certain regions can communicate;
(2) the utilization efficiency of the whole system resource is increased and the system capacity is also increased; and under the same conditions, non-dispatching area group calls will consume more system resource compared to dispatching area group calls given the same number of users; and
(3) a group member in the dispatching area can push to talk (PTT) to communicate with all other group members so that the call connection time is shortened.
Most of the group calls initiated by a trunking communication user terminal are dispatching area group calls. However, a user may not be able to get real-time information from its user terminal about which dispatching area a group belongs to and which groups can call the user. Conventional solution to this problem is to fix dispatching areas and dispatching purposes for certain groups, which have to be memorized by users. However, this method has the problems of low adaptability and low reliability, and in an urgent dispatching scene, the consequences of mal-operation cannot be underestimated.